This switches the static asset check over from the deprecated paver commands to the new 'npm run build' command. Doing so allows us to check both the prod AND dev build, whereas before we were only checking the prod build. Please note that, as before, the "check" is only ensuring that the build returns 0. It is not checking the contents of the build output. Closes: https://github.com/openedx/edx-platform/issues/34834